This invention relates to electrically insulating board.
In my earlier U.S. Pat. No. 4,407,876 I described an electrically insulating wrapping material for electrical machinery comprising high temperature fibres (such as "Nomex"--Registered Trade Mark) in the form of a stitch bonded fabric. Nomex is poly(m-phenyleneisophthalamide), which is an aromatic polyamide, or "aramid." The method of fabrication is inexpensive because it uses mainly fibres and no, or only a little, yarn and yields a flexible wrapping tape which is better adapted to cover the corners of diamond-shaped coils of electrical rotating machinery when used as a wrapped insulation intended for resin impregnation. Hitherto, relatively stiff paper tapes of Nomex fibres have been used for this purpose which have the disadvantage that at such awkward bends as are encountered on coils, the winding `gaped` and left a spot with inadequate insulation. The inherent, textile-type flexibility of the stitch bonded tape overcomes this problem completely.
I have now found that the stitch bonded fabric of high temperature fibres has another use in electrical insulation which however is wholly surprising even over my previous invention.